There are competing objectives in most digital signal processing (DSP) systems which have digital-to-analog converter (DAC) output stages that re-convert a digitally processed signal to an analog signal. On the one hand one wants to keep the system inexpensive and simple, but on the other hand one wants a high performance system. To achieve minimal expense a DSP system uses as low a data sample rate as possible and uses as simple an analog re-construction filter as possible. To achieve higher performance one uses as high a data sample rate as possible and uses a relatively complex analog reconstruction filter. The higher the data sample rate the less the data high frequency components will be attenuated by Sin(x)/x effects and the higher (i.e. easier to filter out) the sampling alias noise product frequencies will be. However, higher data sampling frequencies require more expensive digital circuitry and a higher performance DAC, both of which contribute to cost. The more complex the analog reconstruction filter the more it can avoid phase and amplitude distortion in the reconstructed analog signal and the more it can avoid alias noise product energy contaminating the output signal. As a consequence of the traditional compromises in these factors it is typical that there will be, especially in consumer grade applications, noticeable high frequency attenuation and group delay distortion in the output signal. There will also be more alias noise product energy in the output than would be desirable if cost were not a factor. Even with these degradations in performance, the reconstruction filters still tend to be relatively large, expensive, and awkward to manufacture relative to the other circuits in a DSP system.
Conventionally, the problems described above are addressed by compromising signal quality or compromising economy. The zero sum nature of these competing goals has not been easily avoided. In digital audio systems some benefit has been derived by using 1-bit DACs operating at very high frequencies. A 1-bit DAC is a DAC whose digital input port is only one bit wide, and which provides its output as an oscillating signal having a duty cycle which varies in response to the input value. Such 1-bit DACs have allowed much simpler filters to be used, but at the expense of dramatically more digital circuitry. In video DSP systems such a solution has not been possible because the 1 bit DAC would have to operate at such high frequencies as to be impractical with low cost commercial technology.